Automatic transmission with improved gear arrangement

ABSTRACT

The present disclosure provides an automatic transmission having an input adapted to couple to a torque-generating mechanism and an output coupled to the input. The transmission also includes a first rotating torque-transferring mechanism disposed along a first torque path and coupled to the input. A second rotating torque-transferring mechanism is disposed along a second torque path and is coupled to the input independent of the first torque-transferring mechanism. The transmission includes a plurality of stationary torque-transferring mechanisms, each of which is disposed between the input and output. The transmission includes a first planetary gearset, a second planetary gearset, a third planetary gearset, and a fourth planetary gearset, where each gearset includes a sun gear, a ring gear, and a carrier assembly. Moreover, the carrier assembly of the third planetary gearset is coupled to the output and the sun gear of the fourth planetary gearset.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/715,131, filed Dec. 14, 2012, having the title “AutomaticTransmission With Improved Gear Arrangement” which claims priority toU.S. Provisional Patent Application Ser. No. 61/577,262, filed Dec. 19,2011, both of which are hereby incorporated by reference in theirentirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a gear arrangement for a transmission,and in particular to a planetary gear arrangement for an automotivetransmission having a Polak gear arrangement.

BACKGROUND

A conventional transmission for a powered vehicle can include a gearbox,i.e., gears, synchronizers, dog clutches, clutch plates and reactionplates, a number of automatically selectable gears, planetary gear sets,hubs, pistons, shafts, and other housings. The clutches can bestationary brakes/clutches or rotating clutches. The transmission canhave an internal shaft which rotates one or more clutches or shafts inthe transmission.

The number of clutches and gear schemes can be used to achieve differentgear ratios. Each gear ratio can define a range in which thetransmission operates. A higher numerical gear ratio, for example, canbe achieved at a lower transmission output speed. This can be importantif a vehicle is heavily loaded or requires higher torque to ascend anelevation, for instance. Alternatively, a lower numerical gear ratio canbe achieved at a higher transmission output speed, particularly when avehicle is travelling at higher speeds on a highway. The lower numericalgear ratio can help increase fuel efficiency at these speeds.

To achieve different gear ratios, gear schemes are configured in whichbrakes, clutches, shafts, and gearsets are packaged in a transmission.The gear scheme can include carrier. One or more of the sun gear, ringgear, and carrier can be input or output of the planetary gearset. Themanner in which torque is transmitted through the clutches and gearsetsdetermines the different gear ratios for a given transmission.

In some arrangements, however, a gear step between shifts precludes theshift from being done automatically. Instead, a vehicle operator mayhave to manually shift the transmission from one gear ratio to the nextwith the throttle released because the gear step is too large. Gear stepis defined as the ratio between gear ratios. In transmissions thatinclude a torque converter and lockup clutch, it may also be difficultto apply the lockup clutch due to the increased gear step.

There is a need for a seven-speed, automatic transmission having a geararrangement for automatically selecting gears and which the gearbox isconfigured for minimizing gear step between gear ratios for forward andreverse ranges.

SUMMARY

In an exemplary embodiment of the present disclosure, an automatictransmission includes an input adapted to couple to a torque-generatingmechanism and an output coupled to the input. The transmission alsoincludes a first rotating torque-transferring mechanism disposed along afirst torque path such that the first rotating torque-transferringmechanism is coupled to the input. A second rotating torque-transferringmechanism is disposed along a second torque path such that the secondrotating torque-transferring mechanism is coupled to the inputindependent of the first torque-transferring mechanism. Moreover, thetransmission includes a first stationary torque-transferring mechanism,a second stationary torque-transferring mechanism, a third stationarytorque-transferring mechanism, and a fourth stationarytorque-transferring mechanism, each of which is disposed between theinput and the output. The transmission further includes a firstplanetary gearset, a second planetary gearset, a third planetarygearset, and a fourth planetary gearset, where each gearset includes asun gear, a ring gear, and a carrier assembly. The carrier assembly ofthe third planetary gearset is coupled to the output and the sun gear ofthe fourth planetary gearset.

In one form of this embodiment, the ring gear of the fourth planetarygearset is coupled to the ring gear of the third planetary gearset. Inanother form thereof, a third torque path is at least partially definedby the input, the sun gear of the first planetary gearset, and thecarrier assembly of the first planetary gearset. In a further form ofthis embodiment, the first torque path is at least partially defined bythe input, the first rotating torque-transferring mechanism, the sungear of the second planetary gearset, and the sun gear of the thirdplanetary gearset. The second torque path is at least partially definedby the input, the second rotating torque-transferring mechanism, and thecarrier assembly of the second planetary gearset.

In one aspect of this embodiment, the input and output are disposedalong the same centerline. In another aspect, the carrier assembly ofthe first planetary gearset is coupled to the ring gear of the secondplanetary gearset and the carrier assembly of the second planetarygearset is coupled to the ring gear of the third planetary gearset. In adifferent aspect, the ring gear of the third planetary gearset iscoupled to the carrier assembly of the second planetary gearset, thering gear of the fourth planetary gearset, the carrier assembly of thethird planetary gearset, and the third stationary torque-transferringmechanism.

In another embodiment, an automatic transmission includes an inputadapted to couple to a torque-generating mechanism and an output coupledto the input. The transmission also includes a first rotatingtorque-transferring mechanism and a second rotating torque-transferringmechanism, the first and second rotating torque-transferring mechanismsbeing independently coupled to the input. Moreover, a plurality ofstationary torque-transferring mechanisms is disposed between the inputand the output. The transmission further includes a first planetarygearset, a second planetary gearset, a third planetary gearset, and afourth planetary gearset, where each gearset is coupled to one of theplurality of stationary torque-transferring mechanisms and includes asun gear, a ring gear, and a carrier assembly. The ring gear of thefourth planetary gearset is coupled to the ring gear of the thirdplanetary gearset.

In one aspect of this embodiment, the carrier assembly of the thirdplanetary gearset is coupled to the output and the sun gear of thefourth planetary gearset. In another aspect, the input and output aredisposed along the same centerline. In a different aspect, the carrierassembly of the first planetary gearset is coupled to the ring gear ofthe second planetary gearset and the carrier assembly of the secondplanetary gearset is coupled to the ring gear of the third planetarygearset. In a further aspect, the ring gear of the third planetarygearset is coupled to the carrier assembly of the second planetarygearset, the ring gear of the fourth planetary gearset, the carrierassembly of the third planetary gearset, and the third stationarytorque-transferring mechanism. In a related aspect, the first rotatingtorque-transferring mechanism comprises an applied state and anunapplied state, where in the applied state the first rotatingtorque-transferring mechanism is coupled to the sun gears of the secondand third planetary gearsets. In yet another related aspect, the secondrotating torque-transferring mechanism comprises an applied state and anunapplied state, where in the applied state the second rotatingtorque-transferring mechanism is coupled to the carrier assembly of thesecond planetary gearset.

In a different embodiment of the present disclosure, a gear scheme isprovided for an automatic transmission. The gear scheme includes atransmission input and a transmission output. The gear scheme alsoincludes a first rotating torque-transferring mechanism and a secondrotating torque-transferring mechanism, each being independently coupledto the transmission input. A plurality of stationary torque-transferringmechanisms is disposed between the transmission input and transmissionoutput. The gear scheme further includes a first planetary gearsetcoupled to the first rotating torque-transferring mechanism, the firstplanetary gearset being coupled to one of the plurality of stationarytorque-transferring mechanisms. A second planetary gearset is coupled tothe first planetary gearset and the first rotating torque-transferringmechanism, the second planetary gearset being coupled to one of theplurality of stationary torque-transferring mechanisms. A thirdplanetary gearset is coupled to the second rotating torque-transferringmechanism and the transmission output, the third planetary gearset beingcoupled to one of the plurality of stationary torque-transferringmechanisms. The gear scheme includes a fourth planetary gearset coupledto the third planetary gearset and one of the stationarytorque-transferring mechanisms. The fourth planetary gearset includes aninput and an output and the third planetary gearset includes an inputand an output, the output of the third planetary gearset being coupledto the transmission output and the input of the fourth planetarygearset. Moreover, the output of the fourth planetary gearset is coupledto the input of the third planetary gearset.

In one aspect of this embodiment, the input of the third planetarygearset comprises a sun gear and a ring gear and the output of the thirdplanetary gearset comprises a carrier assembly. The input of the fourthplanetary gearset comprises a sun gear and the output of the fourthplanetary gearset comprises a ring gear, where the ring gears of thethird and fourth planetary gearsets are coupled to one another. Inanother aspect, the transmission input and transmission output aredisposed on the same centerline. In a different aspect, the firstrotating torque-transferring mechanism comprises an applied state and anunapplied state, where in the applied state the first rotatingtorque-transferring mechanism is coupled to a sun gear of the secondplanetary gearset and a sun gear of the third planetary gearset. In analternative aspect, the second rotating torque-transferring mechanismcomprises an applied state and an unapplied state, where in the appliedstate the second rotating torque-transferring mechanism is coupled to acarrier assembly of the second planetary gearset.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects of the present disclosure and the manner ofobtaining them will become more apparent and the disclosure itself willbe better understood by reference to the following description of theembodiments of the disclosure, taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of one embodiment of a transmission coupledto a controller via a wiring harness;

FIG. 2 is a first gear scheme for a seven speed automatic transmission;and

FIG. 3 is a second gear scheme for a seven speed automatic transmission.

Corresponding reference numerals are used to indicate correspondingparts throughout the several views.

DETAILED DESCRIPTION

The embodiments of the present disclosure described below are notintended to be exhaustive or to limit the disclosure to the preciseforms disclosed in the following detailed description. Rather, theembodiments are chosen and described so that others skilled in the artmay appreciate and understand the principles and practices of thepresent disclosure.

The present disclosure relates to a transmission with an improved gearscheme. With reference to FIG. 1, an exemplary embodiment of atransmission assembly is provided. A transmission 102 is shown in FIG. 1with a controller 104, i.e., transmission control module (“TCM”).Software is downloaded to the TCM 104 and a wiring harness 106 couplesthe TCM 104 to the transmission 102. A conventional wiring harness 106includes an outer plastic body that surrounds wires that extend from aTCM connector 110 at one end of the wiring harness 106 to a transmissionconnector 108 disposed at the opposite end of the wiring harness 106.

The wiring harness 106 can also include other connectors such as speedsensor connectors. In FIG. 1, for example, an engine or input speedsensor connector 112 couples to an engine or input speed sensor 126 ofthe transmission 102. Likewise, in an embodiment in which a torqueconverter is present, a turbine speed sensor connector 114 couples thewiring harness 106 to a turbine speed sensor 128 of the transmission102. Also, an output speed sensor connector 116 of the wiring harness106 couples to an output speed sensor 130 of the transmission 102. Otherpossible connectors of the wiring harness 106 include a data busconnector 120, a throttle position sensor (TPS) 124, a vehicle connector118 (e.g., Vehicle Interface Module (“VIM”) connector), and analternative transmission harness mating connector 122. There can beadditional connectors and/or harnesses in other embodiments.

As noted, the transmission 102 can include the engine or input speedsensor 126, turbine speed sensor 128, and output speed sensor 130. Inthis embodiment, the transmission 102 mounts to an engine (not shown) bycoupling a converter housing 134 of the transmission 102 to a flywheelhousing (not shown) of the engine (not shown). A torque transferringmechanism 132, e.g., a torque converter or fluid coupling, of thetransmission 102 can include a plurality of lugs 140 that couple to aflex plate (not shown) via flex plate bolts (not shown). For purposes ofthis embodiment, the torque-transferring mechanism 132 will be referredto as a torque converter. In some embodiments, a torque converter maynot be present. In these embodiments, an input shaft of the transmission102 is coupled to the engine via a clutch, for example.

In one embodiment, an internal combustion engine (not shown) can becoupled to the transmission 102 via the torque converter 132 (or inputshaft for those embodiments without a torque converter). The internalcombustion engine can be configured to rotatably drive an output shaft(not shown) of the engine that is coupled to the input (not shown) ofthe torque converter 132. The torque converter 132 can further include aturbine (not shown) that is coupled via splines to a turbine shaft (notshown) of the transmission 102. In turn, the turbine shaft (not shown)can be coupled to, or integral with, a rotatable input shaft (not shown)of the transmission 102. An output shaft (not shown) of the transmission102 can be coupled to or integral with, and rotatably drives, apropeller shaft (not shown) that is coupled to a conventional universaljoint (not shown). The universal joint (not shown) can be coupled to,and rotatably drives, a drive axle (not shown) having tires or wheelsmounted thereto at each end. The output shaft (not shown) of thetransmission 102 drives the tires in a conventional manner via thepropeller shaft, universal joint and drive axle.

During operation, as the engine rotatably drives the torque converter132, the engine or input speed sensor 126 detects the rotational speedof the torque converter 132. The torque converter 132 can include ribsor protrusions (not shown) that protrude from the surface of the torqueconverter 132 and which the engine or input speed sensor 126 measuresduring each revolution.

As shown in FIG. 1, the transmission 102 can also include a main case orhousing 136 that encloses a gearbox, i.e., gears, synchronizers, brakes,dog clutches, clutch plates and reaction plates, a number ofautomatically selectable gears, planetary gear sets, hubs, pistons,shafts, and other housings. The transmission 102 can further include aturbine shaft (not shown) which can rotate various clutches or shafts inthe transmission. A gear or tonewheel (not shown) can be coupled to theturbine shaft (not shown) such that the turbine speed sensor 128, whichcouples to the main case or housing 136, measures the rotational speedof the gear or tonewheel (not shown). Other transmissions can includealternative ways known to the skilled artisan for measuring turbinespeed.

In one embodiment, the transmission 102 can include an output shaft (notshown) which is enclosed by a rear cover 138 of the transmission 102. Tomeasure the output speed of the transmission 102, the output speedsensor 130 can couple to the rear cover 138. A smaller gear or tonewheel(not shown) can be coupled to the output shaft (not shown) such that theoutput shaft and gear or tonewheel rotate together. The output speedsensor 130 is aligned with the gear or tonewheel and measures therotational speed of the output shaft.

Transmission shift schedules and other related instructions are includedin software which is downloaded to the TCM 104. The TCM 104 can controlthe shifting of the transmission by electrically transferringinstructions to the transmission such that certain actions are carriedout by the synchronizers, brakes, clutches, dog clutches, pistons, etc.In one non-limiting embodiment, the TCM 104 is part of a transmissioncontrol circuit that can further include an electronic solenoid andvalve assembly for controlling the engaging and disengaging of clutchassemblies, etc. Components within the transmission 102 can be activatedelectrically, mechanically, hydraulically, pneumatically, automatically,semi-automatically, and/or manually. The transmission control circuit isable to control the operation of the transmission to achieve desiredperformance.

Based on instructions in a transmission software program, thetransmission control circuit (e.g., TCM 104) can select a shift scheduledepending on a vehicle's driving condition and execute instructionscontained in the software by sending signals through the wiring harness106 to control the transmission 102. The TCM 104 can also receivemeasurement data from the transmission 102 such as, for example, inputspeed from the input speed sensor 126, turbine speed from the turbinespeed sensor 128, and output speed from the output speed sensor 130. Inan embodiment in which the transmission does not include a torqueconverter 132, the transmission may only have an input speed sensor 126and output speed sensor 130. The TCM 104 can also calculate variousparameters including transmission gear ratio or range, which istypically the ratio of input speed to output speed. In an embodiment inwhich the transmission 102 has a torque converter 132, the transmissiongear ratio or range can also be determined by the ratio of turbine speedto output speed.

The TCM 104 can also receive accelerator pedal position (i.e., throttlepercentage) from a throttle input source, which can be coupled to anengine control module (ECM) or vehicle control module (VCM) fortransmitting throttle data over a data bus. Examples of a conventionaldata bus include J1708 data bus, J1939 data bus, IESCAN data bus, GMLAN,Mercedes PT-CAN. In addition, a Hardwire TPS (throttle position sensor)to TCM or Hardwire PWM (pulse width modulation) to TCM can be used.Information such as accelerator pedal position that is communicated overthe data bus is not limited to a particular engine/transmissionconfiguration. Instead, the data bus can be adapted to most vehiclesetups.

With reference to FIG. 2, an exemplary gear scheme 200 is provided fortransferring torque from an input 202 of the transmission to an output204 thereof. As shown, the gear scheme 200 further includes a pluralityof torque-transferring mechanisms. The plurality of torque-transferringmechanisms can include a pair of rotating clutches, i.e., C1 and C2, andfour stationary clutches or brakes, i.e., C3, C4, C5, and C6. Each ofthe clutches or brakes can be arranged in a pack, for example, andinclude one or more plates. The plates can include friction material andthus comprise friction plates, whereas other plates can be disposedbetween the friction plates and are referred to as reaction plates.

The gear scheme 200 can also include a plurality of planetary gearsets.For example, in FIG. 2, the scheme 200 includes a first planetarygearset 206, a second planetary gearset 208, a third planetary gearset210, and a fourth planetary gearset 212. For purposes of thisdisclosure, the first planetary gearset 206 can be referred to as a P1planetary gearset. Likewise, the second, third, and fourth planetarygearsets can be referred to as P2, P3, and P4, respectively. Eachplanetary gearset can include a sun gear, a ring gear, and a carrier.For instance, the P1 planetary gearset 206 includes a P1 sun gear 214, aP1 carrier 216, and a P1 ring gear 218. The P2 planetary gearset 208includes a P2 sun gear 220, a P2 carrier 222, and a P2 ring gear 224.Similarly, the P3 planetary gearset 210 includes a P3 sun gear 226, a P3carrier 228, and a P3 ring gear 230. The P4 planetary gearset 212includes a P4 sun gear 232, a P4 carrier 234, and a P4 ring gear 236.Each of the carriers can include a plurality of planet gears rotatablycoupled thereto.

In FIG. 2, the lines connecting the different components can refer to orindicate paths through which torque is transferred. In addition, wherethe lines are broken (e.g., an “=” sign), this can refer to the couplingof two or more components (e.g., gears, splines, clutch, brakes, etc.)to one another in the gear scheme. For instance, the plurality of planetgears of the P1 carrier 216 are shown being coupled to the P1 sun gear214 and the P1 ring gear 218 (e.g., in a planetary gearset arrangement,the P1 planet gears can be disposed around the P1 sun gear 214 while theP1 ring gear 218 surrounds both the planet gears and sun gear 214). Whenthe C1 or C2 clutch is unapplied, torque cannot pass through eitherclutch. Similarly, when the C3 clutch or brake is applied, for example,the P1 ring gear 218 is held and cannot rotate. From this point forwardin this disclosure, the C1 and C2 torque-transmitting mechanisms will bereferred to as “clutches” and the C3-C6 torque-transferring mechanismswill be referred to as “brakes”, but it is to be understood that thesecomponents may be different in alternative embodiments.

In the present disclosure, the gear scheme 200 is such that two clutches(or two brakes or one clutch and one brake) are applied to achieve aparticular range or gear ratio. In other gear scheme embodiments,however, a range may be achieved by applying any combination of clutchesor brakes (e.g., one clutch, three clutches, four clutches, etc.). Inone particular embodiment, for example, a gear scheme can be definedsuch that a plurality of forward and reverse ranges, their respectivegear ratio (or possible range of gear ratios), and the applied clutchand/or brake for achieving the respective range is as follows:

Applied Clutches or Gear Range Gear Ratio Brakes F1 5.0-9.0 C1 & C6 F22.5-6.0 C1 & C5 F3 1.5-4.5 C1 & C4 F4 1.1-3.0 C1 & C3 F5 0.9-1.1 C1 & C2F6 0.25-0.99 C2 & C3 F7 0.25-0.99 C2 & C4 R2 (−3.0)-(−7.0) C3 & C5 R1 (−7.0)-(−20.0) C3 & C6

In the table above, “F1” refers to a first forward range, “F2” refers toa second forward range, etc. In addition, “R1” refers to a first reverserange and “R2” refers to a second reverse range. The combination of gearratios, ranges, and applied clutches and brakes is only provided aboveas an illustrative example and is not intended to limit the presentdisclosure in any manner. One skilled in the art can appreciatedifferent gear ratios and applying or unapplying different clutchesand/or brakes. Moreover, other embodiments are possible in whichadditional or fewer ranges are possible. The gear ratio can also beadjusted as desired to accommodate a close ratio or wide ratiotransmission. As is known, the difference between a close ratio and wideratio transmission can be defined by the number of gear teeth on thevarious components of the planetary gearsets.

In the first gear scheme 200, the gear step between F1 and F2 may be toolarge for the shift to be performed automatically. Instead, the vehicleoperator may have to manually shift to this higher numerical gear ratiofrom the F2 range to the F1 range with the throttle released. Similarly,the operator would have to manually shift from the F1 range to the F2range. In addition, the F1 to F2 gear step may prevent the shift frombeing made with the torque converter lockup clutch applied, which canresult in higher transmission heat generation.

Referring to FIG. 3, however, a different gear scheme 300 can beprovided for a transmission for automatically shifting between the F1and F2 ranges and the R1 and R2 ranges. Further, the F1 to F2 shift canbe achieved with the torque converter lockup clutch applied.

In the second forward range, F2, of gear scheme 200, the torque paththrough the transmission is such that the C1 clutch and C5 brake areapplied. When the C5 brake is applied, it can substantially lock the P3ring gear 230 from rotating. With the P3 ring gear 230 stopped, the P3sun gear 226 is an input of torque and the P3 carrier 228 is the output.As the skilled artisan understands, the P3 sun gear 226 and P3 carrier228 rotate in the same direction.

Referring to the first forward range, F1, the C6 brake is applied. TheC6 brake acts like a brake and substantially locks the P4 carrier 234from rotating. Thus, as torque passes through the transmission, the P3sun gear 226 and P3 carrier 228 continue rotating in the same directionas described above with respect to forward range F2. Torque passesthrough the P4 carrier 234 with the P4 ring gear 236 being the input andthe P4 sun gear 232 being the output. As noted above, the P4 carrier isheld by the C6 brake.

With the P4 ring gear 236 acting as the input, the P4 sun gear 232rotates in the opposite direction as and at a greater speed than the P4ring gear 236. The P4 sun gear 232 therefore drives the P3 ring gear 230in the opposite direction of the P3 sun gear 226 which reduces thetransmission rotational output speed since the P3 ring gear 230 reducesthe output speed of the P3 carrier 228. Since the relationship of thespeed ratio to the gear ratio is an inverse relationship, a reducedspeed creates a greater gear ratio. For purposes of comparing the gearschemes of FIGS. 2 and 3, the first forward range F1 in gear scheme 200can be referred to as HIGH numerical first ratio.

Turning to FIG. 3, a different embodiment of a gear scheme 300 is shown.Here, the gear scheme 300 provides a transmission input 302, atransmission output 304, and a different arrangement of the P4 planetarygearset 312. The transmission input 302 and transmission output 304 canbe disposed along the same centerline or axis, as shown in FIG. 3.Moreover, the inputs and outputs of the P1 planetary gearset 306, P2planetary gearset 308, and P3 planetary gearset 310 in the gear scheme300 can be substantially similar to that of gear scheme 200. As shown,the gear scheme 300 can include two rotating torque-transferringmechanisms, C1 and C2, and four stationary torque-transferringmechanisms, i.e., C3, C4, C5, and C6. The gear scheme 300 also caninclude a first planetary gearset 306, a second planetary gearset 308, athird planetary gearset 310, and a fourth planetary gearset 312. Thefirst planetary gearset 306, or P1 planetary gearset, can include a P1sun gear 314, a P1 carrier 316, and a P1 ring gear 318. Likewise, thesecond planetary gearset 308, or P2 planetary gearset, can include a P2sun gear 320, a P2 carrier 322, and a P2 ring gear 324. The thirdplanetary gearset 310, or P3 planetary gearset, can include a P3 sungear 326, a P3 carrier 328, and a P3 ring gear 330. Similarly, thefourth planetary gearset 312, or P4 planetary gearset, can include a P4sun gear 332, a P4 carrier 334, and a P4 ring gear 336. Each of thecarriers can include a plurality of planet gears rotatably coupledthereto.

The gear scheme 300 can produce similar ranges, gear ratios, andapplied/unapplied clutches as described above with respect to gearscheme 200. Thus, in second forward range, F2, the C1 clutch and C5brake can be applied. In this embodiment, the P3 ring gear 330 is heldfixed by the C5 brake. Torque therefore passes through the P3 planetarygearset 310 via the P3 sun gear 326 and is output through the P3 carrier328. The P3 sun gear 326 and P3 carrier 328 rotate in the same directionand thus transfer output torque to the transmission output 304.

In the first forward, F1, however, the gear scheme 300 differs over thegear scheme 200. In FIG. 3, the P4 carrier 334 is held fixed by the C6brake. Similar to the second forward range, input through the P3planetary gearset 310 is via the P3 sun gear 326. The P3 sun gear 326transfers torque to the P3 carrier 328 which drives the transmissionoutput 304. The P3 sun gear 326 and P3 carrier 328 rotate in the samedirection and further drive the P4 sun gear 332. With the P4 carrierbeing held, the P4 sun gear 332 drives the P4 ring gear 336. The P4 ringgear 336 rotates in a direction opposite the P4 sun gear 332 and furtherdrives the P3 ring gear 330 in the reverse direction. Although the P4ring gear 336 is driven in the opposite direction by the P4 sun gear332, it also rotates at a slower rotational speed than the P4 sun gear332. Since the P4 ring gear 336 is rotating at a slower speed, the P3ring gear 330 does so as well. Thus, with the P3 ring gear 330 rotatingin the opposite direction compared to the P3 carrier 328, but at aslower speed, the overall speed reduction through the P3 planetarygearset 310 is less than in gear scheme 200. Consequently, the speedratio is not reduced as significantly as gear scheme 200, and the gearratio is substantially less than the HIGH numerical first ratio in gearscheme 200. For purposes of distinction, the first gear ratio of gearscheme 300 can be referred to as LOW numerical first ratio. This doesnot mean that the gear ratio for the first forward range in gear scheme300 is small, but rather it is simply to note that the gear ratio in thefirst forward range in gear scheme 300 is smaller than the gear ratio inthe first forward range in gear scheme 200.

In one aspect, the reduction in gear ratio can be significant such thatthe gear step between the first forward range and second forward rangein gear scheme 300 is small enough that the shift therebetween can beachieved automatically and without releasing the throttle. In addition,the gear step can be small enough that the shift therebetween can bedone while keeping the torque converter lockup clutch applied. This canresult in lower transmission heat generation.

In gear schemes 200 and 300, the torque flow path between thetransmission input 202, 302 and transmission output 204, 304 is similarfor other forward ranges. For instance, in a third forward range F3, theC4 brake holds the P2 ring gear 324 from rotating. Torque thereforepasses through the P2 planetary gearset 308 via the P2 sun gear 320 andis output through the P2 carrier 322. The P2 carrier 322 rotates in thesame direction as the P2 sun gear 320 and is coupled to the P3 ring gear330. Torque also passes through the P3 planetary gearset 310 as an inputvia the P3 sun gear 326. The P3 carrier 328 outputs torque to thetransmission output 304 as shown.

In a fourth forward range F4, the C3 brake can hold the first ring gear318. Torque can therefore enter the P1 planetary gearset 306 via the P1sun gear 314 and output via the P1 carrier 316. The P1 carrier 316 iscoupled to the P2 ring gear 324, and as a result torque passes throughthe P2 planetary gearset 308 through the P2 ring gear 324 (via the P1carrier 316) and the P2 sun gear 320 (with C1 clutch applied). The P2carrier 322 is the output of the P2 planetary gearset 308 and transferstorque to the P3 ring gear 330. Thus, torque passes through the P3planetary gearset 310 via the P3 ring gear 330 (via the P2 carrier) andP3 sun gear 326 (with the C1 clutch applied). The P3 carrier 328 outputstorque to the transmission output 304.

In a fifth forward range F5, the C1 and C2 clutches are applied, butnone of the stationary brakes are applied. Thus, torque from thetransmission input 302 enters the P3 planetary gearset 310 via the P3sun gear 326 (with the C1 clutch applied) and the P3 ring gear 330 (viathe P2 carrier 322). With the P3 sun gear 326 and P3 ring gear 330rotating at input speed, the P3 carrier 328 and transmission output 304rotate at input speed thereby resulting in a gear ratio of approximately1.0.

In a sixth forward range F6, the C2 clutch and C3 brake are applied.Unlike the previously described embodiments, the C1 clutch is notapplied. The C3 brake holds the P1 ring gear 318. Torque thereforepasses through the P1 planetary gearset 306 via the P1 sun gear 314 andis output through the P1 carrier 316. Torque passes through the P2planetary gearset 308 through the P2 ring gear 324 (via the P1 carrier316), P2 carrier 322 (with C2 clutch applied), and the P3 ring gear 330(with the C2 clutch applied). This can overdrive the P2 sun gear 320 andthe P3 sun gear 326 (i.e., causing both to rotate faster). With the P3sun gear 326 being overdriven and the P3 ring gear rotating at inputspeed, the P3 carrier 328 and transmission output 304 are overdriven inthe sixth forward range F6, thereby achieving a gear ratio less than1.0.

In a seventh forward range F7, the C2 clutch and C4 brake are applied.In this range, the C4 brake holds the P2 ring gear 324. Torque is inputto the P2 planetary gearset 308 directly from the transmission input 302to the P2 carrier 322 and P3 ring gear 330. This condition overdrivesthe P2 sun gear 320 and P3 sun gear 326 to a larger degree than thesixth forward range F6. With the P3 sun gear 326 being overdriven to agreater degree (i.e., rotating faster) and the P3 ring gear 330 rotatingat input speed, the P3 carrier 328 and transmission output 304 areoverdriven in the seventh forward range F7 to a larger degree than inthe sixth forward range F6.

In the above-described embodiments, the torque flow paths can differdepending on the gear scheme and which clutches or brakes areapplied/unapplied. In one embodiment, the gear ratio in the firstforward range is greater than the gear ratios for the second, third,fourth, fifth, sixth, and seventh forward ranges. The gear ratio in theseventh forward range is less than the gear ratios in the first, second,third, fourth, fifth, and sixth forward ranges.

The gear schemes 200, 300 are also capable of producing a first andsecond reverse ranges, i.e., R1 and R2 respectively. Again, however, dueto the difference in configurations, the first gear scheme 200 andsecond gear scheme 300 are capable of producing different gear ratios inreverse. In one embodiment, the gear ratio in the second reverse rangeR2 is the same for both gear schemes, but the gear ratio in the firstreverse range R1 is different. In an embodiment in which the number ofgear teeth differs between the two gear schemes, the gear ratio in thefirst and second reverse ranges can be different.

Referring to FIG. 2, the second reverse range R2 can be achieved byapplying the C3 and C5 brakes. Both of these brakes are stationary andhold ring gears from rotating. Specifically, the C3 brake holds the P1ring gear 218 and the C5 brake holds the P3 ring gear 230. Since neitherthe C1 nor C2 clutches are applied, torque is transferred from thetransmission input 202 to the first planetary gearset 206 via the P1 sungear 214. Since the P1 ring gear 218 is held, the P1 carrier 216 rotatesin the same direction as the P1 sun gear 214, albeit at a slower speed,and transfers torque to the P2 planetary gearset 208 via the P2 ringgear 224.

Since the C5 brake holds the P3 ring gear 230, the P2 carrier 222 cannotrotate. As such, the P2 sun gear 220 is the output of the P2 planetarygearset 208. Since the P2 carrier 222 is held, the P2 ring gear 224 andP2 sun gear 220 rotate in opposite directions relative to each other,but with the P2 sun gear 220 rotating at a higher speed than the P2 ringgear 224. With the P2 sun gear 220 now rotating in an opposite directionfrom the transmission input 202, the P2 sun gear 220 drives the P3 sungear 226 in the opposite direction of the transmission input 202 aswell. The P3 sun gear 226 continues to drive the P3 carrier 228 in theopposite direction of the transmission input 202, albeit at a slowerspeed, and thus the transmission output 204 (which is driven by the P3carrier 228) rotates in the reverse direction.

In FIG. 2, the P3 carrier 228 is coupled to the P4 ring gear 236. Theoutput of the P4 planetary gearset 212 is the P4 carrier 234, butbecause the P4 carrier 234 is not driving another element (i.e., sincethe C5 brake is holding the P3 ring gear 230 from rotation), there is noeffect on the transmission output 204 by the P4 planetary gearset 212.As such, when the C3 and C5 brakes are applied in gear scheme 200, thetransmission output 204 is in a second reverse range R2.

A first reverse range, R1, is achieved similarly as the second reverserange, R2, except the C6 brake is applied rather than the C5 brake. Thisresults in the P4 carrier 234 being held instead of the P3 ring gear230. With the P4 carrier being held, the P4 ring gear 236 is rotating inreverse and drives the P4 sun gear 232 and the P3 ring gear 230 in theforward direction (i.e., opposite the P4 ring gear 236). Given the P3sun gear 226 is rotating in reverse, rotating the P3 ring gear 230forward instead of holding it fixed can result in the P3 carrier 228 andtransmission output 204 rotating slower in the reverse direction in thefirst reverse range R1 compared to the second reverse range R2.Therefore, the magnitude of the numerical gear ratio in the firstreverse range, R1, is greater than the numerical gear ratio in thesecond reverse range, R2.

In the embodiment of FIG. 3, the gear scheme 300 can also provide afirst reverse range R1 and a second reverse range R2. The torque path inthe second reverse range R2 is substantially similar as described abovein gear scheme 200. The gear ratio in the second reverse range R2 can bedefined by the number of gear teeth in the P1 planetary gearset 306, P2planetary gearset 308, and P3 planetary gearset 310. In the firstreverse range R1, however, the coupling of the P3 planetary gearset 310and P4 planetary gearset 312 can produce a gear ratio that is less thanthe gear ratio in first reverse range R1 for the first gear scheme 200.

Referring to FIG. 3, the P1 ring gear 318 is held by the C3 brake andthe P4 carrier 334 is held by the C6 brake, which is similar to thefirst reverse range R1 of the first gear scheme 200. However, thedifferent manner in which the P4 sun gear 232 and P4 ring gear 236 areconnected in the gear scheme 200 relative to the gear scheme 300 resultsin numerical gear ratios in the first reverse range, R1, which aredifferent for each gear scheme. In gear scheme 300, for example, thereverse direction input to the P4 planetary gearset 312 is the P4 sungear 332 rather than the P4 ring gear 236 of gear scheme 200. Thisresults in the output of the P4 planetary gearset 312 (e.g., P4 ringgear 336) and the P3 ring gear 330 rotating slower in the forwarddirection than that of the P3 ring gear 230 of gear scheme 200. Giventhe P3 sun gear 326 is rotating in reverse, the slower rotation of theP3 ring gear 330 in the forward direction than in gear scheme 200results in the P3 carrier 328 and transmission output 304 rotatingfaster in the reverse direction than in gear scheme 200. Therefore, themagnitude of the numerical gear ratio in the first reverse range, R1, ofgear scheme 300 is less than the magnitude of the numerical gear ratioof the first reverse range, R1, of gear scheme 200. The gear stepbetween the first reverse range, R1, and second reverse range, R2, ofgear scheme 300 is also less than that of gear scheme 200.

The gear step between the first reverse range, R1, and second reverserange, R2, can be reduced for the second gear scheme 300 regardless ofwhether a close ratio or wide ratio transmission is being used. Thus,the transmission can automatically shift between the two reverse rangeswithout requiring any interaction on behalf of the vehicle operator,e.g., such as releasing the throttle and/or bringing the vehicle to astop first.

In those embodiments in which the shift between the first forward rangeand second forward range can be achieved automatically, anotheradvantage can include improved life of the planetary gearsets. When thegear step is large between ranges, the gear teeth in the planetarygearsets are subject to higher loads and wear more quickly. However,smaller gear steps can improve the durability and robustness of the gearteeth and thus extend the life of the planetary gearsets. This can alsolead to less downtime for the vehicle as fewer repairs are required.

In addition, a lockup clutch in a torque converter can be appliedbetween a first forward range and second forward range due to a smallergear step. This can improve the transmission efficiency, reducetransmission heat generation, and improve performance during shifts. Asa result, the improved gear scheme 300 can improve transmission shiftquality, wear and performance over a transmission arranged in accordancewith the second gear scheme 200.

While exemplary embodiments incorporating the principles of the presentdisclosure have been disclosed hereinabove, the present disclosure isnot limited to the disclosed embodiments. Instead, this application isintended to cover any variations, uses, or adaptations of the disclosureusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this disclosure pertains andwhich fall within the limits of the appended claims.

The invention claimed as:
 1. An automatic transmission, comprising; aninput adapted to couple to a torque-generating mechanism; an outputcoupled to the input; a first rotating torque-transferring mechanismdisposed along a first torque path, the first rotatingtorque-transferring mechanism being coupled to the input; a secondrotating torque-transferring mechanism disposed along a second torquepath, the second rotating torque-transferring mechanism being coupled tothe input independent of the first torque-transferring mechanism; afirst stationary torque-transferring mechanism, a second stationarytorque-transferring mechanism, a third stationary torque-transferringmechanism, and a fourth stationary torque-transferring mechanism, eachof the stationary torque-transferring mechanisms being disposed betweenthe input and the output; and a first planetary gearset, a secondplanetary gearset, a third planetary gearset, and a fourth planetarygearset, where each gearset includes a sun gear, a ring gear, and acarrier assembly; wherein, the carrier assembly of the third planetarygearset is coupled to the output and to the ring gear of the fourthplanetary gearset; wherein, the carrier assembly of the first planetarygearset is coupled to the ring gear of the second planetary gearset;wherein, the input is directly coupled to the first planetary gearset.2. The automatic transmission of claim 1, wherein the carrier assemblyof the second planetary gearset is coupled to the ring gear of the thirdplanetary gearset.
 3. The automatic transmission of claim 1, furthercomprising a third torque path at least partially defined by the input,the sun gear of the first planetary gearset, and the carrier assembly ofthe first planetary gearset.
 4. The automatic transmission of claim 1,wherein the first torque path is at least partially defined by theinput, the first rotating torque-transferring mechanism, the sun gear ofthe second planetary gearset, and the sun gear of the third planetarygearset.
 5. The automatic transmission of claim 1, wherein the secondtorque path is at least partially defined by the input, the secondrotating torque-transferring mechanism, and the carrier assembly of thesecond planetary gearset.
 6. The automatic transmission of claim 1,wherein the input and output are disposed along the same centerline. 7.The automatic transmission of claim 2, wherein the ring gear of thethird planetary gearset is coupled to the carrier assembly of the secondplanetary gearset, to the sun gear of the fourth planetary gearset, tothe carrier assembly of the third planetary gearset, and to the thirdstationary torque-transferring mechanism.
 8. The automatic transmissionof claim 7, wherein the carrier assembly of the first planetary gearsetis coupled to the second stationary torque mechanism.
 9. An automatictransmission, comprising: an input adapted to couple to atorque-generating mechanism; an output coupled to the input; a firstrotating torque-transferring mechanism and a second rotatingtorque-transferring mechanism, the first and second rotatingtorque-transferring mechanisms being independently coupled to the input;a plurality of stationary torque-transferring mechanisms disposedbetween the input and the output; and a first planetary gearset, asecond planetary gearset, a third planetary gearset, and a fourthplanetary gearset, where each gearset is coupled to one of the pluralityof stationary torque-transferring mechanisms and includes a sun gear, aring, gear, and a carrier assembly; wherein, the carrier assembly of thethird planetary gearset is coupled to the output and to the ring gear ofthe fourth planetary gearset; and wherein the carrier assembly of thefirst planetary gearset is coupled to the ring gear of the secondplanetary gearset; wherein, the input is directly coupled to the sungear of the first planetary gearset.
 10. The automatic transmission ofclaim 9, wherein the input and output are disposed along the samecenterline.
 11. The automatic transmission of claim 10, wherein thecarrier assembly of the second planetary gearset is coupled to the ringgear of the third planetary gearset.
 12. The automatic transmission ofclaim 11, wherein the ring gear of the third planetary gearset iscoupled to the carrier assembly of the second planetary gearset, to thesun gear of the fourth planetary gearset, and to the third stationarytorque-transferring mechanism.
 13. The automatic transmission of claim12, wherein the carrier assembly of the first planetary gearset iscoupled to the second stationary torque mechanism.
 14. The automatictransmission of claim 9, wherein the first rotating torque-transferringmechanism comprises an applied state and an unapplied state, where inthe applied state the first rotating torque-transferring mechanisminterconnects the input to the sun gears ofthe second and thirdplanetary gearsets.
 15. The automatic transmission of claim 9, whereinthe second, rotating torque-transferring mechanism comprises an appliedstate and an unapplied state, where in the applied state the secondrotating torque-transferring mechanism interconnects the input to thecarrier assembly of the second planetary gearset.
 16. A gear scheme foran automatic transmission, comprising: a transmission input and atransmission output; a first rotating torque-transferring mechanism anda second rotating torque-transferring mechanism, each beingindependently coupled to the transmission input; a plurality ofstationary torque-transferring mechanisms disposed between thetransmission input and transmission output; a first planetary gearsetdirectly coupled to the transmission input, the first planetary gearsetbeing coupled to one of the plurality of stationary torque-transferringmechanisms; a second planetary gearset coupled to the first planetarygearset and the first rotating torque-transferring mechanism, the secondplanetary gearset being coupled to one of the plurality of stationarytorque-transferring mechanisms; a third planetary gearset coupled to thesecond rotating torque-transferring mechanism and the transmissionoutput, the third planetary gearset being coupled to one of theplurality of stationary torque-transferring mechanisms; and a fourthplanetary gearset coupled to the third planetary gearset and one of thestationary torque-transferring mechanisms; wherein, the fourth planetarygearset includes an input and an output and the third planetary gearsetincludes an input and an output, the output of the third planetarygearset being coupled to the transmission output and the output of thefourth planetary gearset; wherein, the output of the fourth planetarygearset is coupled to a carrier assembly of the third planetary gearset,and wherein a carrier assembly of the first planetary gearset is coupledto a ring gear of the second planetary gearset; wherein, thetorque-transferring mechanisms are selectively engageable incombinations of at least two establish at least seven forward gearratios and at least one reverse gear ratio between the transmissioninput and the transmission output, where in the least one reverse gearratio neither rotating torque-transferring mechanism is selectivelyengaged and the transmission input is directly coupled to a sun gear ofthe first planetary gearset.
 17. The gear scheme of claim 16, wherein:the input of the third planetary gearset comprises a sun gear and a ringgear and the output of the third planetary gearset comprises a carrierassembly; and the input of the fourth planetary gearset comprises a sungear and the output of the fourth planetary gearset comprises a ringgear, where the ring gear of the third planetary gearset is coupled tothe sun gear of the fourth planetary gearset.
 18. The gear scheme ofclaim 16, wherein the transmission input and transmission output aredisposed on the same centerline.
 19. The gear scheme of claim 16,wherein the first rotating torque-transferring mechanism comprises anapplied state and an unapplied state, where in the applied state thefirst rotating torque-transferring mechanism interconnects thetransmission input to a sun gear of the second planetary gearset and asun gear of the third planetary gearset.
 20. The automatic transmissionof claim 19, wherein the second rotating torque-transferring mechanismcomprises an applied state and an unapplied state, where in the appliedstate the second rotating torque-transferring mechanism interconnectsthe transmission input to a carrier assembly of the second planetarygearset.